This invention relates to a fuel injector arrangement and to a method of operating a fuel injector arrangement. The term injector arrangement is intended to cover mixing devices wherein fluid fuel and air are mixed to form a mixture to be burnt in combustion apparatus, e.g. turbines, engines, burners etc, and the term thereby covers inter alia carburetor and burner mixer arrangements. The invention is particularly suited to gas-fuelled lean-burn combustor arrangements.
FIG. 1 illustrates a conventional fuel injector arrangement comprising a housing which defines a chamber positioned in an annular airstream conduit 10. The housing 1 is defined by side walls 2, 3 and an end wall 4 and acts as a fluid fuel plenum 5 to which fluid fuel is supplied via a circular-section conduit 6 which is surrounded by the annular conduit 10. It should be understood that the housing 1 may inter alia take the form of a fuel post extending radially outwardly from the fuel conduit 6 with suitable interconnection therebetween for fuel to flow from conduit 6 to plenum 5 and there will generally be a plurality of such posts arranged around the conduit 6; in alternative realizations the housing 1 will be of annular or part-annular form extending around the whole or part of the circumference of the fuel conduit 6. In any event the housing 1 is formed with a plurality of radially and/or circumferentially spaced holes 7 or arrays of holes 7 through which jets of fuel pass into an airstream 11 which flows through the conduit 10 surrounding plenum 5 and which passes around and past the housing 1 to thereby entrain the fuel into the airstream 11. Conduit 10 conventionally contains blades 8 to swirl the airstream. The fuel and air mix together as the air moves downstream from the housing 1 to form a combustible mixture which is burnt in a combustion chamber 14.
This conventional arrangement suffers from a number of disadvantages. To ensure uniform distribution of the fuel and air there must be a large number of the holes 7 and thus each hole will be of small area. This means that the manufacturing techniques involve precise tolerances and also mean that, in use, the holes are prone to blockage through the build-up of deposits. With holes blocked in this way poor entrainment of fuel and inefficient combustion of the fuel will result. Furthermore, small holes limit the penetration of fuel into the airstream and thus restrict the efficiency of the fuel/air mixing process.
The present invention aims to provide a fuel injector arrangement which overcomes these disadvantages.